Browning reaction amino acids

The significance of small amounts of metals to the Maillard reaction appears to have been first studied by Webb169 in 1935, in his work on the color of evaporated milk. The browning of lactose solutions at 49° was found to be positively catalyzed by copper and iron, but retarded by tin. Traces of cupric salts similarly accelerate the browning of amino acids or proteins with D-glucose in weakly alkaline solutions, but they have no ef-... 

In our investigation on the effect of Maillard reaction products on the absorption of tryptophan (36), the kinetics of the absorption of tryptophan in the presence of Maillard reaction products formed in the glucose-tryptophan system was studied by bott vitro everted gut sac method and vivo catherization of the portal vein. Fructose-L-tryptophan (Amadori compound) appeared to be the major fraction of the reaction products when fractionated using a cellulose column eluted by water-saturated n-butanol. The absorption of L-tryptophan was partially inhibited vitro and vivo by fructose-L-tryptophan in a competitive manner with an inhibitor constant (Ki) of l.lmM. The relative absorption rate of L-tryptophan was significantly lower in the presence of the Maillard reaction products than in the presence of fructose-L-tryptophan indicating the presence of other inhibitory factors in the reaction products. The in vivo absorption of fructose-L-tryptophan was almost negligible compared to that of tryptophan. The inhibited absorption by Maillard reaction products, may have contributed in part to an incomplete recovery in the growth of the rats when fed a supplemented browned synthetic amino acid diet. 

Browning aids amino acids and reducing sugars, e.g., fructose and dextrose (Maillard reaction)... 

MaillardReaction (Nonenzymatic Glycation), Browned reaction products ate formed by heating amino acid and simple sugar. This reaction is important in food science relating to coloring, taste, and flavor enhancement (79), and is iUustrated as follows ... 

Amino acids play a role in food processing in the development of a cooked flavor as the result of a chemical reaction called the nonenzymatic browning reaction (228). 

A quote from a biochemistry text is instructive here. "This is not an easy reaction in organic chemistry. It is, however, a very important type of reaction in metabolic chemistry and is an integral step in the oxidation of carbohydrates, fats, and several amino acids." G. L. Zubay, Biochemistry, 4th ed., William C. Brown Publishers, 1996, p. 333. 

Monosaccharides are probably involved in the browning reactions that occur during the roasting of coffee. Caramelization involving the sugars alone, and Maillard reactions, between sugars and free amino acids, produce polymeric yellow to dark brown substances, known as melanoidins. These melanoidins can be extracted into hot water, separated and characterized.105... 

ROS can modify amino acid side chains, with histidine, tryptophan, cysteine, proline, arginine, and lysine among those most susceptible to attack (Brown and Kelly 1994). As a result, carbonyl groups are generated, and these carbonyl concentrations can be measured directly in plasma by using atomic absorption spectroscopy, fluorescence spectroscopy, or HPLC following reaction with 2,4-dinitrophenylhydrazine. 

Browning caused by Maillard-type reactions between carbohydrates and amino acids or caramelisation contribute to appearance, taste and flavour of many products. Carbohydrate sweeteners are important for these reactions, and other types of sweetening agents may not react in a similar way, therefore rendering products more pale. 

The factors affecting the Maillard reaction include temperature, time, moisture content, concentration, pH, and nature of the reactants. - It has been shown that, out of 21 amino acids, glycine, lysine, tryptophan, and tyrosine provide the most intense browning when exposed to five saccharides, especially a-lactose. The Maillard reaction is also responsible for the decreased availability of lysine in proteinaceous foods. 

Heyns K, Heukeshoven J and Brose KH (1968) Degradation of fructose amino acids to N-(2-furoylmethyl)amino acids. Intermediates in the browning reaction. Angew Chem Int Ed 7, 628-629. 

Numerous review articles (1-20) and a number of books (21-26) have been devoted to the Maillard reaction, viz., the non-enzymatic browning reactions involving amino acids and reducing sugars. 

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